Every day about 280 billion red blood cells (RBCs) are produced in the bone marrow to ensure oxygen transport throughout the entire body1. Erythropoiesis is a finely tuned differentiation process that produces mature, functional red blood cells from hematopoietic stem cells. Many diseases, both acquired and congenital, can affect this process, including myelodysplastic syndrome, aplastic anemia, thalassemia, and congenital dyserythropoietic anemia2.
The clinical manifestation of disrupted erythropoiesis is anemia, a major cause of morbidity worldwide. Symptoms of anemia range from fatigue, shortness of breath, and dizziness to life-threatening conditions, such as heart failure and cardiac arrest3.With anemia affecting 1.8 billion people worldwide4, modeling erythropoiesis ex vivo in order to investigate these conditions and their underlying mechanisms remains a global priority. The method described here aims to provide a simple and robust model for studying both healthy and diseased erythroid differentiation. This model allows for the dissection of the roles of specific genes in this process and enables the testing of compounds that could benefit anemic patients. Historically, modeling ineffective erythropoiesis has had many challenges, including a paucity of stem cells in some diseased bone marrows and difficulties mimicking the bone marrow niche.
Previous studies have used similar or more complex protocols; for instance, Bondu et al. used a cocktail of cytokines including erythropoietin (EPO), stem cell factor (SCF), and interleukin-6 (IL6) for 4 days before removing IL6 from the cocktail of erythroid differentiation, in contrast, Yip et al. only added EPO to their cytokines cocktail after 7 days of liquid culture. Elvarsdóttir et al. developed a three-dimensional (3D) culture model for CD34+ cells to facilitate the highest expansion and maturation of erythroid cells, including the generation of erythroblastic islands and enucleated erythrocytes, which are important to study phenomena such as ring sideroblasts5,6,7,8. This protocol uses only three cytokines when expanding the cells (i.e., SCF, thrombopoietin [TPO], and FMS-like tyrosine kinase 3 [FLT3]) and three cytokines maintained throughout the whole process of differentiation (i.e., EPO, IGF1, and SCF). One of the key criteria shared across these different studies is the use of CD34+ cells. Although the origin of these cells varies, they are consistently employed across these different protocols. The sources might range from non-invasive collection of UCB to more invasive procedures to obtain adult bone marrow samples that can be harvested either from granulocyte colony-stimulating factor (G-CSF) mobilized patients or bone marrow punctures. In general, liquid culture models are carried over 14 days, while 3D models can maintain cells over longer periods. These protocols are essential for modeling genetic diseases and disruptions in erythropoiesis. Genetic approaches, such as short hairpin RNA (shRNA) knockdowns, can be employed to silence genes of interest and study their roles in erythropoiesis. The impact of gene silencing can then be monitored at various stages of differentiation, providing an ex vivo human model of red blood cell production to study anemia in both health and disease. This protocol includes the transduction of CD34+ cord blood cells with shRNA that constitutively express a reporter gene, such as enhanced green fluorescence protein (EGFP), allowing the samples to be sorted by fluorescence-activated cell sorting (FACS). Cells are then incubated in differentiation media for 2 weeks and monitored by flow cytometry analysis and immunochemistry staining.